1. Field of the Invention
The present invention relates to a method of separating iron sheets from wasted iron products, which are parts of wasted electric products such as air-conditioners or refrigerators.
2. Description of the Prior Art
Recently, in view of environmental protection, many attempts have been made to recycle ferrous material from wasted iron products that constitute a part of electric products such as air-conditioners or refrigerators. However, because of low selecting accuracy and low recycling efficiency of the conventional recycling systems, obtained cast material is used only as lower-class iron material.
In the conventional iron recycling methods, wasted iron products are crushed into pieces and iron pieces are magnetically separated therefrom. Collected iron pieces are thrown into a furnace and recycled as cast material. However, when separating the iron scraps from the crushed pieces, sheet-shaped iron scraps and iron cast blocks are not distinguished and collected together. Therefore, when they are thrown into the furnace, the heavy cast blocks fall downwardly into the furnace, but the light-weight ferrous sheets are apt to be blown up by a hot blast within the furnace. The blown-up ferrous sheets are not reused and enter into an inhaling mechanism of the furnace, which may cause a mechanical trouble of the furnace.
Further, thin sheet-shaped scraps are torn and pressed in the crushing process to have a twisted shape. Scraps shaped in such a manner are apt to wind around other scraps, which make it difficult to separate the scraps. Accordingly, it is preferable that the sheet-shaped scraps are separated in an early step of the recycling.
To solve these problems, the U.S. patent application Ser. No. 09/456838, for example, describes a recycling method as follows: First, only sheet-shaped scraps are magnetically separated, and then, ferrous cast blocks are magnetically separated from the crushed pieces of the wasted iron products. Among the separated cast blocks, relatively light ones are sandwiched by the sheet scraps and pressed together. The combined ferrous piece has enough weight to be thrown into the furnace without flying up by the hot blast in the furnace. Thus, iron material can be recycled safely and with high efficiency. Also, since the sheet-shaped scraps are separated in an early step of the recycling, the entwining of the scraps is prevented. The sheet-shaped scraps can be selectively separated by controlling the magnetic flux density of the conventional magnetic separator.
The reason why the sheet-shaped scraps can be selectively separated is as follows: A capability of attracting the ferrous pieces by the magnetic separator depends on a difference between magnetic and gravitational force applied on the ferrous piece. The magnetic force on the ferrous piece depends on a magnetic flux density and a surface area of the ferrous piece. Since the sheet-shaped scraps are torn and pressed in the crusher to have a long and twisted shape, the sheet-shaped iron scraps have larger surface areas than those of the cast iron blocks. Accordingly the magnetic force applied on the sheet-shaped scrap is stronger than that on the same-weight cast block. Therefore, an adequate control of the magnetic flux density leads to selective attraction of the sheet-shaped iron scraps.
FIG. 3 shows a process for selectively separating the sheet-shaped iron scraps from crushed pieces of the iron products. The crushed pieces 14, including iron sheet pieces 16, cast iron blocks 18 and non-iron pieces 20, are transported on a conveyer 10, such as a vibrating conveyer. A magnetic separator 12 is placed over the conveyer 10 and set to provide an adequate magnetic flux density so that the iron sheet pieces 16 can be selectively attracted. Among the crushed pieces 14 moving from the right side in the figure, only the iron sheet pieces 16 are attracted by the magnetic separator 12. The rest of the pieces 14, the cast blocks 18 and non-ferrous pieces 20, are carried to the next step, in which the cast blocks 18 are separated.
In this method, the sheet-shaped iron pieces 16 are selectively attracted by utilizing the difference in the surface area per weight. However, because of a variation in the shapes of the iron sheet pieces 16, in some cases, the magnetic force may become equal to the gravitational force on the iron sheet pieces 16. Accordingly, some of the iron sheet pieces 16 are apt to remain on the conveyer 10. The presence of these residual iron sheet pieces 16 not only decreases the recycling efficiency but also causes problems as set forth below.
The residual sheet pieces 16 are affected by the magnetic force to stay under the magnetic separator 12, and wind around the cast blocks 18 and the non-ferrous pieces 20 carried after the residual sheet pieces 16. This causes a jam on the conveyer 10 and prevents a smooth operation of the recycling system. Further, the entwining between the iron sheet pieces 16 and other pieces makes it difficult to separate them in the following steps.
Most of the residual sheet pieces 16 eventually move forward with other crushed pieces 14 and they are attracted with the cast blocks 18 in the next magnetic separating step. On the other hand, a part of the residual iron sheet pieces 16 lose the balance between the magnetic and gravitational force by collision with other pieces and they are attracted by the magnetic separator 12 along with light-weight non-ferrous pieces 20 such as copper wires. Thus, some iron sheet pieces 16 are mixed in the collected cast blocks 18, and some non-ferrous pieces 20 are mixed in the collected iron sheet pieces 16. The mixing of the iron sheet pieces 16 with the cast blocks 18 gives an unfavorable influence to the sandwich-press process of the cast blocks 18. The mixing of the non-ferrous pieces 20 with the iron sheet pieces 16 reduces the purity of the recycled cast material.
It is accordingly an object of the present invention to provide a method of separating iron sheets from wasted iron products wherein the iron sheets are smoothly recycled with high efficiency.
According to the present invention, a method of separating iron sheets from wasted iron products comprises the steps of:
crushing wasted iron products into pieces;
transporting said crushed pieces on a conveyer;
separating iron sheet pieces from said crushed pieces on said conveyer by means of a magnetic separator placed over said conveyer, wherein said iron sheet pieces staying on said conveyer in a standing state are selectively subjected to an upward force.
By applying the upward force to the sheet-shaped iron pieces staying on the conveyer, the balance between the magnetic and gravitational force is lost and the sheet-shaped pieces are smoothly attracted by the magnetic separator. Thus, the remaining sheet-shaped pieces on the conveyor are prevented and the recycling efficiency of the iron material is improved.
The upward force is preferably applied by hitting an upper portion of the iron sheet piece with an upwardly directed force. The iron sheet piece staying on the conveyer is in a standing state under the balance of magnetic and gravitational force. Accordingly, the iron sheet piece staying on the conveyer is taller than other crushed pieces. Utilizing this difference in the height between the iron sheet piece and other pieces, it becomes possible to hit the upper portion of the iron sheet piece selectively. In order to break the balance of the magnetic and gravitational force on the iron sheet piece, only a little force is required.
In order to hit the iron sheet piece, a variety of means can be employed. For example, a rotor placed so as to hit the upper portion of the iron sheet pieces may be used. The rotor is preferably rotating in an inverse direction relative to the moving direction of the conveyer so that the upward force is effectively applied to the iron sheet pieces. Alternatively, a pendulum may be employed to hit the iron sheet pieces.
The rotor or pendulum is preferably placed under the magnetic separator and near the end of the magnetic separator. With this arrangement, the iron sheet pieces are hit toward an attracting area of the magnetic separator. Also, this arrangement broadens the attracting area of the iron sheet pieces. Accordingly, the attraction of the iron sheet pieces becomes smooth.
In this specification, the term xe2x80x9cwasted iron productsxe2x80x9d means wasted products composed of iron-based metal or wasted products having a lot of such metal parts.